US2029451A - Electrolytic condenser - Google Patents

Description

Feb. 4, 1936. w. c. VAN GEEL ET! AL 2,029,451

ELECTROLYTIC CONDENSER Filed Feb. 25, 1932 INVENTORS WILLEM CHRISTIAAN VAN GEEL BY 'HIEEIQMMENS ATTORNEY Patented. Feb. 4, 1936 UNITED STATES 2,029,451 I nmoraow'nc oonnsnssa Willem Christiaan van Geei and Hendrik Emmens, Eindhoven, Netherlands, assignors to Radio Corporation of America, a corporation oi Delaware Application February 25, 1932, Serial No. 594,982 In the Netherlands June 20, 1931 5 Claims.

This invention relates to improvements in electric condensers.

It is an object of this invention to simplify and improve the construction of electrolytic condensers so that the life of the condenser is increased.

In the customary construction of electrolytic condensers one electrode of such a condenser consists of a metal plate or a metal wire coated by electrolytic or chemical agency with an oxide coating and immersed in an electrolyte constituting the other electrode. For this purpose the electrolyte is furnished with a conductor for the supply of the electric current, said conductor being formed, for example, by the wall of the vessel in which the electrolyte is enclosed.

One of the difliculties which have to be overcome with such condensers is the attack of the oxide coating so that the life of the condenser is limited.

Now it has been found that this attack is to be imputed to a large extent to impurities enclosed in the electrolyte. Even when during the manufacture of the condenser a careful watch is kept that no impurities occur in the electrolyte, it is found that in the course of time they nevertheless occur. Indeed, they are absorbed from the wall of the vessel or are due to the insulating parts which are used for taking the conductors through the wall of the vessel, said insulators containing in general organic material.

Even when use is made of electrolytes consisting of solutions of solid substances in alcohol, such as glycerol, which electrolytes otherwise have favourable properties with regard to leakage current and capacity, it is found that said disadvantage is not disposed of without additional means.

This has only been found possible by using a solution of one or more of the primary or secondary phosphates in an alcohol, for example of primary potassium phosphate in glycerol. This combination has been found to permit of the oxide coating of the metal electrodes being protected from attack.

Perhaps this striking action is to be imputed to the circumstance that it is found possible to dissolve a great deal of the solid substance primary potassium phosphate in the glycerol sothat consequently the proportion of the quantity of impurity in the liquid becomes negligible relatively to the quantity of the substance dissolved in addition and also the influence of the impurities decreases thereby accordingly. In this case the circumstance that in spite of the large quantity of primary potassium phosphate which is dis- 5 solved the conductivity does not become great plays an important part since in most dissolved substances in which the quantity of the substance dissolved is comparatively large the conductivity of the electrolyte becomes great as well and incl 10 dental thereto is an inadmissable leakage current. However, this phenomenon does not occur in the said use of primary potassium phosphate.

Favourable results were obtained with a condenser one electrode of which was of aluminium, 15 whereas the electrolyte consisted of pure glycerol -having added to it 50 grams of primary potassium phosphate (KH2PO4) per liter.

Similarly, good results were obtained when this electrolyte had added to it in addition 10% of 20 water.

When, for example, a solution of primary potassium or sodium phosphate is used, this solution is acid. Now, a further protection of the electrodes from attack can be obtained by adding to the solution a basicly reacting phosphate, for example secondary potassium or sodium phosphate, in such a proportion that the solution is just neutral.

In order that the invention may be clearly understood and readily carried into efiect a condenser in accordance therewith will now be described more fully with reference to the accompanying drawing.

Referring to the drawing, a copper vessel l contains an electrolyte 2 consisting of pure glycerol in which primary potassium phosphate is dissolved in a proportion of 50 grams per liter of glycerol. On its upper side the vessel is closed by an ebonite disc 3 through which the end of an 40 aluminium wire 4 is taken. In order to obtain a large surface area, the aluminium wire is wound helically. A plurality of such helices might be arranged one within the other. Leading-in wires may be connected to 5 and 6. The aluminium wire is coated by chemical or electrolytic agency with an oxide coating which constitutes the insulating intermediate layer between the electrodes of the condenser.

A condenser as illustrated in the dram'ng is only suitable for smoothing direct current as it disrupts the current only in one direction. It can therefore be used as a rectifier as well. If such condensers are desired to be used for alternating current, a second aluminium electrode similarly coated With an oxide coating may be arranged in the electrolyte and the two aluminium electrodes may be connected to the terminals of the alternating current supply.

Various modifications are otherwise possible without departing from the scope of the invention. Thus, for example, the aluminium wire may be profiled in order to increase the surface area and instead of wire use may be made of rolled-up plates the windings of which are kept apart by distance holders.

Alternatively, the electrolyte may have added to it over 10% of water. Even with of water good results have still beenobtained.

We claim:

1. An electrolytic condenser comprising a metallic electrode, an oxide coating on said metallic electrode, an electrolyte consisting of a solution of acid phosphate, and alcohol of the group including glycerol, for the purpose of preventing an attack on said oxide coating.

2. An electrolytic condenser comprising a metallic electrode, an oxide coating on said metallic electrode, and an electrolyte having the properties of preventing an attack on the oxide coating of said electrode, consisting of a solution of primary potassium phosphate in glycerol to which solution is added substantially 10% of water.

3. An electrolytic condenser comprising a metallic electrode of alum num having an oxide coating, and an electroL'fie consisting of a solution of pure glycerol in which primary potassium phosphate is dissolved in a quantity of grams per liter.

4. An electrolytic condenser comprising a copper vessel containing an electrolyte of pure glycerol in which primary potassium phosphate is dissolved, an insulating disc enclosing said vessel, and an electrode of aluminum wire having an oxide coating which constitutes an insulating layer between the condenser electrode.

5. An electrolytic rectifier comprising a copper vessel containing an electrolyte of pure glycerol in which primary potassium phosphate is dissolved, an insulating disc enclosing said vessel, and two electrodes of aluminum wire having an oxide coating which constitutes an insulating layer between the rectifier electrodes.

WILLEM CHRISTIAAN VAN GEEL. HENDRIK EMMENS.

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